The subject matter of the invention is a new process for the production of L-proline from an L-pyroglutamic acid ester.
There are already known various processes for the production of L-proline from the methyl or ethyl ester of pyroglutamic acid. The known processes, however, produce L-proline only in small yields.
It is also known already to produce L-proline through the reaction of free L-pyroglutamic acid with triethyloxonium-tetrafluoroborate and subsequent reduction of the iminoether obtained with sodium borohydride (Synthesis 1974, page 137). As the yield there is given 75%. Apart from the fact that this yield could not be reproduced by other authors (see e.g. D. Enders et al, in Chem. Ber. Vol. 112, pages 3703-3714, especially page 3714 (1979), footnote 19), the triethyloxonium tetrafluoroborate which is needed in great excess is very difficult to handle so that converting this process to an industrial scale does not appear possible.